A new study used whole-genome bisulphite sequencing to map the epigenome of senescent cells and to show that they have similar methylation marks to those in cancer cells. Aberrant methylation has been associated with tumorigenic changes in gene expression, such as silencing of tumour suppressors and constitutive activation of growth-promoting genes. Thus, the authors conclude that the similarities between the methylome of senescent cells and tumour cells is significant, as senescent cells that escape replicative senescence are genomically unstable and primed for transformation.